The dumbbell is a form of free weight and is a very common piece of fitness equipment that is ... predominantly used for resistance training. Dumbbells are very useful as they can target each side of the body independently which results in less muscular imbalances that often occur with barbell use. A dumbbell is essentially a common piece of gym equipment that consists of a short bar and a weighted dumbbell head at each end of the bar. There are three main types of dumbbells which are known as adjustable dumbbells, fixed-weight dumbbells, and selectorized dumbbells. All forms of dumbbells can be used for both commercial and home gym workouts.